1. Field of the Invention
The present invention relates to a double-mass type dynamic damper having two secondary vibration systems which are tuned to different frequency ranges, and to a drive shaft equipped with such a double-mass type dynamic damper.
2. Discussion of Related Art
As a type of vibration damping device for reducing vibrations of a rod-shaped oscillating member, such as a shaft, arm or a conduit for forming a fluid passage, used in various mechanical apparatus, there is known a dynamic damper as disclosed in JP-A-2-62442 or JP-A-2-190641, which has a cylindrical mass member disposed radially outwardly of the oscillating member, and an elastic support member for elastically supporting the mass member for connection thereof with the oscillating member.
The dynamic damper of this type exhibits an excellent damping effect with respect to vibrations in a frequency range corresponding to the natural vibration frequency of the damper. To achieve a desired vibration damping effect, therefore, the mass of the mass member and the spring constant of the elastic support member are controlled so that the natural vibration frequency of the dynamic damper is tuned with high accuracy, depending upon the frequency range of the vibrations of the the oscillating member, which are to be damped by this damper.
However, the natural vibration frequency is tuned to a single frequency range, and the dynamic damper is only able to effectively damp vibrations in a narrow or limited frequency range corresponding to the natural vibration frequency. It is thus difficult for the known dynamic damper to provide high damping effects with respect to a plurality of kinds of vibrations applied to the dynamic damper.
When the vibration acceleration of the oscillating member varies, in such a case where the oscillating member in the form of a drive shaft of an automobile generates greatly varying oscillating forces depending upon the running condition of the automobile, for example, the amplitude of the oscillating mass member of the dynamic damper is varied, and the spring constant of the elastic support member is accordingly changed. Consequently, the natural vibration frequency of the dynamic damper is shifted or changed, resulting in reduced damping effects with respect to the vibrations to be damped by the damper.